Semiconductor light-emitting device with layers having different band gaps

Abstract

A semiconductor light-emitting device fabricated as a double hetero-structure InGaAsP/InP-type laser. The laser includes a buffer layer made of a semiconductor. The buffer layer is located at the upper edge of the flow region of electrons as seen from the active layer. The conductivity type of the buffer layer is opposite to that of a clad layer located at the upper edge of the flow region of electrons seen from the buffer layer. A, the band gap of the buffer layer is wider than that of the active layer but narrower than that of a clad layer adjacent to the buffer layer. The thickness of the buffer layer does not exceed the diffusion length of the electrons injected into the buffer layer.

We claim: 
     
       1. A semiconductor light-emitting device fabricated as a double hetero-structure InGaAsP/InP-type laser comprising: a semiconductor substrate;   an active layer having a band gap;   first and second clad layers each having a band gap; between which said active layer is sandwiched, said first clad layer of a first conductivity type and said second clad layer of a second conductivity type opposite to that of the first conductivity type having therein a region of electron flow with an upper edge and a diffusion length;   a buffer layer, comprising a semiconductor material, located at the upper edge of said region of electron flow, between said first clad layer and said active layer, said buffer layer being of the second conductivity type and having a band gap, said band gap of said buffer layer being wider than that of said active layer but narrower than said band gap of said first clad layer, said buffer layer having a thickness which does not exceed a diffusion length of the electrons.   
     
     
       2. A device as set forth in claim 1, wherein said active layer comprises p type InGaAsP, wherein said buffer layer comprises p type InGasP, wherein said first clad layer comprises n type InP, and wherein said second clad layer comprises p type InP. 
     
     
       3. A device as set forth in claim 1, further comprising a current-restriction layer, mounted on one of said first and second clad layers, said current restriction layer defining a current path region which extends into said corresponding clad layer. 
     
     
       4. A device as set forth in claim 1, wherein said semiconductor substrate has a V-shaped groove formed therein, and wherein said active layer, said buffer layer, and said first and second clad layers comprise a multilayer, formed in the V-shaped groove in said semiconductor substrate, in which said active layer and said buffer layer are sandwiched between said first and second clad layers. 
     
     
       5. A semiconductor light-emitting device, comprising: a first electrode;   a substrate of a first conductivity type formed on said first electrode;   a first clad layer of the first conductivity type formed on the substrate and having a first band gap;   a semiconductor buffer layer of a second conductivity type formed on said first clad layer and having a second band gap narrower than the first band gap of said first clad layer;   an active layer of the second conductivity type formed on the semiconductor buffer layer having a third band gap narrower than the second band gap of said semiconductor buffer layer;   a second clad layer of the second conductivity type formed on said active layer;   a current restriction layer of the first conductivity type formed on said second clad layer;   a current path region of the second conductivity type formed in said current restriction layer; and   a second electrode formed on said current restriction layer and said current path region.   
     
     
       6. A device as set forth in claim 5, wherein electrons having a diffusion length are injected into said semiconductor buffer layer and wherein said semiconductor buffer layer comprises a thickness less than or equal to the diffusion length of said electrons.